CIGS, or Copper Indium Gallium Selenide (or Sulfur “S”), is a I-III-VI group compound semiconductor. Elements from these groups are especially attractive for solar applications because of their high optical absorption coefficients and versatile optical and electrical characteristics, which can in principle be manipulated and tuned for a specific need in a given device. CIGS is one of three mainstream thin-film PV technologies, the other two being cadmium telluride and amorphous silicon. A direct bandgap material, CIGS has very strong light absorption and a layer of only 1-2 micrometers (μm) is enough to absorb most of the sunlight. By comparison, a much greater thickness of about 160-190 μm is required for crystalline silicon wafers (not crystalline silicon thin-film which only requires up to 30 μm). Recently, many in the solar cell R&D community have concluded that a multi-junction or tandem solar cell is the best solution to solving the problem of solar cell efficiency and bringing costs down. Combining a thin-film of CIGS with a thin inorganic film, such as silicon or germanium, which has a lower bandgap than CIGS (or CGS), would make an ideal tandem device. Yet this has not been achieved. The present invention offers a way to achieve this that is simple, cost-effective, and non-toxic.